This invention relates generally to a method and apparatus for checking and/or correcting alignment of a vehicle frame, body or various parts thereof.
Repairing frame damage in a car is a difficult proposition. If a car is in a head-on collision, the undercarriage frame elements on which the sheet metal is mounted is pushed out of alignment. This must be precisely realigned prior to outerbody repair. The principal frame alignment tool that is conventionally used for this purpose is known in the car repair industry as a ladder or rack system. One such ladder system is sold by Buske Industries of Gowrie, Iowa and includes a series of rails running longitudinally beneath the automobile, lateral rails slidably mounted along the longitudinal rails, and expandable measuring gauges mounted to the lateral rails for movement beneath the automobile. The rails form a horizontal datum line or plane beneath the automobile so that accurate measurements between the rails and the automobile frame can be obtained using the gauges. Other such systems are disclosed in U.S. Pat. No. 4,683,663 to Sarauer, U.S. Pat. No. 4,691,443 to Hamilton et al., and U.S. Pat. No. 5,341,575 to Chisum.
In use, the ladder system is placed underneath the automobile and pointers on the gauges brought upward into engagement with predetermined vehicle datum points on the car frame. The three dimensional positions of these vehicle datum points relative to one another are predetermined by manufacturing specifications. The rails and gauges are calibrated such that the pointers can be positioned where one would expect to find a vehicle reference datum point. If the vehicle datum points on the frame are not aligned with the pointers on the ladder system, then the frame is misaligned and must be pulled by suitable pull means so as to bring the datum point into its correct position above the pointer.
The disadvantages of such ladder systems in that the equipment is bulky (about the size of the automobile itself) and extremely expensive thus putting it out of reach of many automobile repair shops. Additionally, the ladder system is a complicated piece of machinery that can take as long as 2 hours or more to set up in preparation for frame straightening.
More sophisticated laser gauging apparatus have been developed recently for measuring a vehicle during repair or construction. These gauging apparatus usually involve mechanically mounting a laser on a rail system or to the vehicle frame. The laser projects a beam of light underneath the vehicle, thus forming a horizontal datum line or plane from which datum point measurements can be taken. Such systems are disclosed in U.S. Pat. No. 4,630,379 to Wickmann et al., U.S. Pat. No. 5,207,002 to Humblet and U.S. Pat. No. 5,515,613 to Hinson. Each require complicated mounting systems that, though potentially more accurate than ladder systems, do not necessarily decrease the time required to set up the equipment and perform the analysis.
Accordingly, a need remains for a simpler more affordable alternative to frame alignment systems known in the prior art.